Repeated Measurements Of Cerebral Blood Flow Research Articles

Variable Temporal Cerebral Blood Flow Response to Acetazolamide in Moyamoya Patients Measured Using Arterial Spin Labeling.

Cerebrovascular reserve capacity (CVR), an important predictor of ischaemic events and a prognostic factor for patients with moyamoya disease (MMD), can be assessed by measuring cerebral blood flow (CBF) before and after administration of acetazolamide (ACZ). Often, a single CBF measurement is performed between 5 and 20 min after ACZ injection. Assessment of the temporal response of the vasodilation secondary to ACZ administration using several repeated CBF measurements has not been studied extensively. Furthermore, the high standard deviations of the group-averaged CVRs reported in the current literature indicate a patient-specific dispersion of CVR values over a wide range. This study aimed to assess the temporal response of the CBF and derived CVR during ACZ challenge using arterial spin labeling in patients with MMD. Eleven patients with MMD were included before or after revascularisation surgery. CBF maps were acquired using pseudo-continuous arterial spin labeling before and 5, 15, and 25 min after an intravenous ACZ injection. A vascular territory template was spatially normalized to patient-specific space, including the bilateral anterior, middle, and posterior cerebral arteries. CBF increased significantly post-ACZ injection in all vascular territories and at all time points. Group-averaged CBF and CVR values remained constant throughout the ACZ challenge in most patients. The maximum increase in CBF occurred most frequently at 5 min post-ACZ injection. However, peaks at 15 or 25 min were also present in some patients. In 68% of the affected vascular territories, the maximum increase in CBF did not occur at 15 min. In individual cases, the difference in CVR between different time points was between 1 and 30% points (mean difference 8% points). In conclusion, there is a substantial variation in CVR between different time points after the ACZ challenge in patients with MMD. Thus, there is a risk that the use of a single post-ACZ measurement time point overestimates disease progression, which could have wide implications for decision-making regarding revascularisation surgery and the interpretation of the outcome thereof. Further studies with larger sample sizes using multiple CBF measurements post-ACZ injection in patients with MMD are encouraged.

Factors of Delayed Hyperperfusion and the Importance of Repeated Cerebral Blood Flow Evaluation for Hyperperfusion After Direct Bypass for Moyamoya Disease

Postoperative hyperperfusion is an important complication after direct bypass for moyamoya disease, which sometimes occurs late after initial postoperative cerebral blood flow (CBF) measurement. This study aimed to clarify the incidence of hyperperfusion with management using postoperative continuous sedation and repeated postoperative CBF measurement and to identify factors associated with delayed hyperperfusion. This retrospective study evaluated 72 consecutive hemispheres in 56 adult Japanese patients with moyamoya disease who underwent direct bypass. Postoperative continuous sedation was routinely administered based on CBF evaluation. First, the incidence of symptomatic hyperperfusion was investigated. Second, radiologic hyperperfusion (RHP), which was strictly defined as >30% increase in CBF compared with the contralateral side, and factors associated with delayed RHP were statistically analyzed. Postoperative symptomatic hyperperfusion occurred in 3 hemispheres (4.2%), including subarachnoid hemorrhage in 1 hemisphere (1.4%). RHP immediately after surgery was identified in 16 hemispheres (22.2%). In 8 hemispheres (11.1%), RHP appeared or worsened several days after initial CBF study. In univariate logistic regression analysis, decreased preoperative cerebral vasoreactivity was significantly associated with delayed RHP. The incidence of symptomatic hyperperfusion was 4.2% with management. Delayed hyperperfusion was significantly associated with decreased cerebral vasoreactivity. Therefore, repeated CBF measurements evaluating preoperative cerebral vasoreactivity may decrease complications.

Estimation of intersubject variability of cerebral blood flow measurements using MRI and positron emission tomography

To investigate the within and between subject variability of quantitative cerebral blood flow (CBF) measurements in normal subjects using various MRI techniques and positron emission tomography (PET). Repeated CBF measurements were performed in 17 healthy, young subjects using three different MRI techniques: arterial spin labeling (ASL), dynamic contrast enhanced T1 weighted perfusion MRI (DCE) and phase contrast mapping (PCM). All MRI measurements were performed within the same session. In 10 of the subjects repeated CBF measurements by (15) O labeled water PET had recently been performed. A mixed linear model was used to estimate between subject (CV(betw)) and within subject (CV(with)) coefficients of variation. Mean global CBF, CV(betw) and CV(with) using each of the four methods were for PCM 65.2 mL/100 g/min, 17.4% and 7.4%, for ASL 37.1 mL/100 g/min, 16.2% and 4.8%, for DCE 43.0 mL/100 g/min, 20.0%, 15.1% and for PET 41.9 mL/100 g/min, 16.5% and 11.9%, respectively. Only for DCE and PCM a significant positive correlation between measurements was demonstrated. These findings confirm large between subject variability in CBF measurements, but suggest also that in healthy subjects a subject-method interaction is a possible source of between subject variability and of method differences.

Magnetic resonance imaging quantification of regional cerebral blood flow and cerebrovascular reactivity to carbon dioxide in normotensive and hypertensive rats

Hypertension afflicts 25% of the general population and over 50% of the elderly. In the present work, arterial spin labeling MRI was used to non-invasively quantify regional cerebral blood flow (CBF), cerebrovascular resistance and CO(2) reactivity in spontaneously hypertensive rats (SHR) and in normotensive Wistar Kyoto rats (WKY), at two different ages (3 months and 10 months) and under the effects of two anesthetics, α-chloralose and 2% isoflurane (1.5 MAC). Repeated CBF measurements were highly consistent, differing by less than 10% and 18% within and across animals, respectively. Under α-chloralose, whole brain CBF at normocapnia did not differ between groups (young WKY: 61 ± 3ml/100g/min; adult WKY: 62 ± 4ml/100g/min; young SHR: 70 ± 9ml/100g/min; adult SHR: 69 ± 8ml/100g/min), indicating normal cerebral autoregulation in SHR. At hypercapnia, CBF values increased significantly, and a linear relationship between CBF and PaCO(2) levels was observed. In contrast, 2% isoflurane impaired cerebral autoregulation. Whole brain CBF in SHR was significantly higher than in WKY rats at normocapnia (young SHR: 139 ± 25ml/100g/min; adult SHR: 104 ± 23ml/100g/min; young WKY: 55± 9ml/100g/min; adult WKY: 71 ± 19ml/100g/min). CBF values increased significantly with increasing CO(2); however, there was a clear saturation of CBF at PaCO(2) levels greater than 70mmHg in both young and adult rats, regardless of absolute CBF values, suggesting that isoflurane interferes with the vasodilatory mechanisms of CO(2). This behavior was observed for both cortical and subcortical structures. Under either anesthetic, CO(2) reactivity values in adult SHR were decreased, confirming that hypertension, when combined with age, increases cerebrovascular resistance and reduces cerebrovascular compliance.

Measurement of cerebral blood flow in newborn infants using near infrared spectroscopy with indocyanine green.

Cerebral blood flow (CBF) measurement by near infrared spectroscopy (NIRS) using oxyhemoglobin (HbO2) as a tracer (CBF-HbO2) needs rapid changes in arterial oxygen saturation (SaO2) which often cannot be achieved in many sick infants. An alternative method based on the same adaptation of the Fick principle using i.v. injection of the dye indocyanine green (ICG) is described (CBF-ICG). Six mechanically ventilated infants (age 26-38 wk, birth weight 0.885-3.730 kg) requiring supplementary oxygen therapy were studied within 72 h of birth. For CBF-ICG measurements, ICG (0.1 mg x kg-1 was injected via an umbilical venous catheter, and blood ICG concentration was measured by an optical umbilical artery catheter and brain ICG concentration was measured by NIRS. For CBF-HbO2 measurements the inspired oxygen concentration was rapidly increased, blood HbO2 concentration was calculated from SaO2 measured by pulse oximetry, and brain HbO2 concentration was measured by NIRS. A series of CBF measurements were performed using each method before and after altering the arterial carbon dioxide tension (PaCO2). Mean CBF values from repeated measurements by each method at any given PaCO2 were used to compare the methods. The SD of single measurements within an individual subject by CBF-ICG was 15%, and by CBF-HbO2, 24%. The relationship between the methods was mean CBF-ICG = (1.13 x mean CBF-HbO2) - 2.76 mL x 100 g-1 x min-1 HbO2 (r = 0.93, p < 0.001). The mean difference between the methods (CBF-ICG - CBF-HbO2) was -0.25 mL x 100 g-1 x min-1 (95% confidence interval 6.30 to -6.80). The methods were in good agreement, and the use of i.v. ICG permitted rapid and repeated CBF measurements in the sickest infants at greatest risk of cerebral injury.

Cerebral Blood Flow and Autoregulation During Hypothermic Cardiopulmonary Bypass

Mean hemispheric cerebral blood flow (CBF) was studied following intravenous or intraarterial administration of xenon-133, in 10 men admitted for coronary-artery bypass grafting. Repeated CBF measurements were performed to evaluate autoregulation before, during, and after cardiopulmonary bypass (CPB). During CPB mean CBF remained unchanged compared with the pre-CPB level, without evidence of cerebral hyperemia or impairment of autoregulation. A marked increase in CBF occurred after CPB and was followed by a time-dependent reduction toward the pre-CPB level. The data support the α-stat regulation theory but cannot explain the cerebral vasodilation observed after CPB.

Prediction and prevention of delayed ischemic dysfunction after aneurysmal subarachnoid hemorrhage and early operation.

Mean hemispheric cerebral blood flow (CBF) was studied after the intravenous administration of xenon-133 in 20 anesthetized patients with aneurysmal subarachnoid hemorrhage. Before early aneurysm operation, repeated CBF measurements were made to evaluate the cerebral vascular reactivity to controlled hyperventilation. Thirteen individuals received intravenous treatment with the calcium channel blocker nimodipine, whereas the other seven patients did not receive such specific antiischemic treatment. Five of the latter patients had an impaired CO2 response, and three showed delayed ischemic deterioration (DID), whereas none of the seven nimodipine-treated patients with impaired CO2 response showed DID. One nimodipine-treated patient with a preserved CO2 response, in whom operation was complicated, developed DID. The observed findings indicate that DID after uncomplicated early aneurysm operation may be associated with an early disturbance of cerebral vasoreactivity. Treatment with nimodipine may counteract the development of DID in patients with an impaired CBF CO2 response.

Lithium carbonate has no measurable effect on cerebral hemodynamics in cluster headaches.

SYNOPSISAny effects of lithium carbonate (oral dosage 900 mg/day) on measurements of cerebral hemodynamics were examined in 10 carefully selected patients meeting criteria of chronic cluster headache, i.e., headache‐free intervals were less than 3 weeks in duration per year. Cerebral blood flow (CBF) was measured by the 133Xe inhalation method before and 2‐4 weeks after (mean 3 weeks) standard recommended lithium carbonate administration, as a dose of 300 mgs give orally three times per day (total 900 mg/24 hours).Cerebral vasoconstrictor responsiveness was tested by repeated CBF measurements during serial inhalations of 100% O2 followed by 5% CO2 in air mixtures. Mean values for hemispheric gray matter flow were 70.9 ml/100g brain/min measured over the side of the cluster headaches and 70.0 ml over the contralateral side prior to lithium and 68.0 ml for sides of the head after lithium treatment. These differences before and after treatment were not significant. Cerebral vasodilator responsiveness to 5% CO2 was expressed as per cent gray matter flow change per mmHg change of measured PECO2 . Compared to values measured in normal age‐matched controls, CO2 responsiveness was diminished bilaterally, both prior to and during lithium administration and there were no significant changes induced after treatment with the drug. Likewise cerebral vasoconstrictor responses during 100% oxygen inhalation were not altered by lithium treatment.